Integral shafts having a flange on one end, which will be referred to as flanged shafts, are used in a variety of mechanical applications. For example, and more specifically, such flanged shafts may comprise the rear axles of rear wheel drive automobiles or the output shafts used in vehicle transmissions.
Flanged shafts are typically manufactured from raw forgings, typically supplied by forging houses or companies, such as the forging 1 illustrated in FIG. 1. Such forgings are typically created by upsetting one end of a shaft 2 to create a flange 3. The shaft 2 has a shaft end 4 and a center axis 5. The flange 3 has two sides, an inboard side 6a and an outboard side 6b. The flange 3 also has a perimeter 7.
For decades, since at least the advent of the rear wheel drive automobile, flanged shafts have been manufactured from such raw forgings using the same three step method.
First, the forging is placed in a center drill and milling machine. More specifically, the unfinished shaft 2 of the raw forging is placed within a centering vise, thereby positioning the center axis 5 of the forging 1 radially in the center drill and milling machine. The forging 1 is positioned axially within the center drill and milling machine by butting the unfinished inboard side 6a or the unfinished outboard side 6b of the flange 3 against a flange stop of the machine.
At that point, the centering vise is locked onto the shaft 2 and the center drill and milling machine is operated. A milling tool mills the shaft end 4 of the forging 1 to a desired length; a flange center drill drills a flange bore in the outboard side 6b of the flange 3; and a shaft center drill drills a shaft bore in the shaft end 4 of the shaft 2. Because the forging 1 is positioned axially based on butting an unfinished flange side 6a or 6b against a flange stop, the axial depth of the central drilled flange and shaft bores are dependent on the surface configuration of the unfinished flange side 6a or 6b being used as a reference point. Likewise, because the forging 1 is positioned radially based on locking the centering vise against the unfinished shaft 2, the radial position of the center drilled flange and shaft bores are dependent on the surface configuration of the unfinished shaft 2. The radial and axial position of the center drilled bores are very important because they are used as reference points in the traditional method during the following steps in order to orient the forging 1 both axially and radially.
To complete the first step, the centering vise is loosened and the forging 1 is removed from the center drill and milling machine.
In the second step, the forging 1 is machined between centers on a lathe. First and second centers are advanced into the center drilled holes on the shaft end 4 and the outboard side 6b of the forging 1, respectively, to position the forging 1 both axially and radially relative to the lathe. A chuck, such as a 3-jaw or 4-jaw chuck, is used to clamp the forging 1, typically on the flange 3 or the shaft 2. After turning the forging 1 by rotating the forging 1 at a high speed and applying a cutting tool to the surfaces desired to be finished, the forging 1 is then released from the chuck and the first and second centers.
In the third step, the forging 1 is turned end for end and machined again between the centers on a lathe. First and second centers are again locked into the center drilled holes on the outboard side 6b and the shaft end 4 of the forging 1, respectively, to position the forging 1 both axially and radially. The forging 1 is again clamped in a chuck and turned by rotating the forging 1 at high speed. A cutting tool is applied to the surfaces desired to be finished which could not be finished by the cutting tool in the second step. The forging 1 is then released from the chuck and the centers and the resulting flanged shaft can proceed through further finishing and heat treatment procedures if desired.
The disadvantages inherent in this traditional method are several. First, and most obviously, the center drilled bores drilled in the first step, which establish the reference points for positioning the forging 1 in subsequent steps, are themselves referenced from the raw surface of the unfinished forging. As a result, surface and geometrical deviations in the raw forging as supplied will result in a defective flanged shaft which must be scrapped. For example, if the flange 3 of the forging 1 is not perpendicular to the center axis 5, or if the flange is thicker than it should be, the butting of the inboard side 6a or the outboard side 6b of the flange 3 against the flange stop of the center drill and milling machine will not position the forging 1 in the correct axial position. As a result, the shaft end 4 will be milled to the wrong dimension and, more importantly, the center drilled flange and shaft bores used as reference points in the subsequent steps will be either too shallow or too deep. Therefore, the forging 1 will not be located in the correct axial position during the following steps 2 and 3 and the resulting flanged shaft will not be manufactured properly and will have to be scrapped.
A second resulting disadvantage is that the raw forgings must be supplied within specific critical tolerances. If not, because the traditional method is referenced from the unfinished surface of the raw forging, the resulting flanged shaft will be defective as previously explained.
Another disadvantage of the traditional method is that flanged shafts cannot be manufactured within certain tolerances. Even when the raw forgings 1 are supplied within the normal tolerances traditionally requested, there will always be inherent variations resulting from the forging process. Because the initial milling and center drilling operations are referenced from a surface of the forging in its raw state, these variations will result in variations of a similar magnitude in the finished flanged shafts.
Another problem with the traditional method is that the operations are interdependent. More specifically, because the first step of milling and center drilling establishes the reference points used in the following operations while also milling the shaft end 4, the subsequent steps will result in a defective flanged shaft if the milling and center drilling is not done properly.